The invention relates generally to the area of machine controls and specifically provides a method and apparatus for automatically locating a cutting tool in close proximity to a workpiece.
Historically, machine control development has been primarily oriented to automating and improving the quality of the machining operation, i.e. those machine operations by which a cutting tool is required to produce a finished part within a specified period of time. However, various surveys indicate that in many manufacturing facilities, production machining operations are being performed on the workpiece approximately only 30% of the time that the machine is manned. Consequently, during most of the time, a machine is idle and is not being used to perform useful work. A significant portion of this time is consumed by set-up procedures which are required to establish particular machine parameters associated with a particular part.
Many set-up procedures require that the cutting tool be placed in close proximity with the workpiece. For example, some set-up procedures require that the cutting tool be moved while it is immediately adjacent to the workpiece. Other set-up procedures require that the cutting tool be located close to the workpiece to check alignments, squareness, taper, etc. Further set-up procedures may require that superficial contact between the cutting tool and the workpiece be used to identify the location of the working edge of the cutting tool from which other cutting tool positions may be measured. This is particularly important on a grinding machine because the location of the working edge is not easily predetermined and is constantly changing.
With traditional machine control systems, and in particular grinding machine controls, the set-up mode is a purely manual operation. All cutting tool motion is under the manual control of the operator, and these controls provide either selectable fixed incremental displacements or continuous motion at selectable feedrates. In either case, the process of bringing a cutting tool into close proximity with the workpiece is a delicate, skillful and time consuming set-up operation. Further, the operator must physically be close to the interface between the cutting tool and the workpiece in order to visually detect the superficial contact.
Consider, for example, a grinding machine having the large mass of a grinding wheel rotating at a high angular velocity with coolant flooding the cutting surface. In order to bring the wheel into superficial contact with the workpiece, the operator is provided with selectable feedrates for controlling the motion of the grinding wheel. The length of the traverse required by the cutting tool may be several inches. The faster feed rates tend to provide a rapid motion that is difficult to judge as the cutting tool approaches the workpiece. The slower feedrates are typically very slow and require excessive periods of time to move the cutting tool short distances. Further, as the wheel nears the workpiece, the flood of coolant hides the area of interface between the cutting tool and the workpiece thereby inhibiting the operator's capability of detecting the superficial contact. Consequently, the seemingly simple task of bringing a grinding wheel into close proximity with the workpiece is a time consuming operation that requires significant skill and care.
Therefore, an object of the invention is to provide an automatic set-up cycle of operation for quickly moving a cutting tool into close proximity with the workpiece without requiring a high level of operator skill.
Another object of the invention is to quickly and easily locate the cutting tool and the workpiece in a predetermined positional relationship during the set-up mode from which a subsequent machining cycle of operation may begin.
A further object of the invention is to automatically align the working edge of the cutting tool relative to the workpiece.
A still further object of the invention is to automatically establish a reference with respect to the working edge of the cutting tool so that subsequent tool motion may be measured with respect to the cutting edge.